Magnesium hydroxide, Mg(OH).sub.2, is useful in various chemical processes including, but not limited to, the following: pH adjustment; precipitation of heavy metal contaminants; scrubbing and neutralization of acidic vapors such as those associated with flue gases or process off-gases; the production of specialty magnesium compounds; and so forth.
So long as they are sufficiently stable, slurries represent an effective and convenient form by which magnesium hydroxide can be furnished. For example, stabilized slurries of magnesium hydroxide have many advantages over other forms of magnesium hydroxide, including the ability to be easily handled, transferred and stored, and the ability to be reliably dosed to chemical processes as desired.
Magnesium hydroxide may typically be derived from three basic sources: seawater, well brines and magnesite ore. In a preferred process, a magnesium hydroxide slurry, is produced from the chemical reaction of dolime (CaO.MgO) and well brine. The well brine comprises primarily calcium chloride but also includes magnesium chloride. The chemical reaction of dolime and well brine produces a slurry of magnesium hydroxide in a chloride-containing liquor. The slurry is then further processed to reduce chloride levels, typically to less than about 0.5%, and to increase solids content, typically to between about 30% and 60%. Unless indicated otherwise, all percentages in this application are weight percentages.
The above slurries, however, have a limited shelf life with respect to stability. First, even with agitation, thickening (i.e., increased viscosity) can occur. In addition, if the material is not agitated, the magnesium hydroxide solids will, after a period of time, typically about 1 to 4 hours, form a hard mass. The hard mass is resuspendable with great effort when dealing with small containers (e.g., up to approximately 5 gallons). However, the hard mass cannot, for all practical purposes, be resuspended when dealing with large containers (e.g., storage tanks, rail cars, trucks), due to the extreme amounts of energy required for such large volumes.
Moreover, in many applications, processing, storage and transportation costs are quite significant. In an attempt to reduce these costs, the above slurry is typically processed to increase the solids content to about 50-60% to reduce water content. However, even after boosting the solids content to these levels, the slurry still contains substantial amounts of water, giving the material added weight and volume, and thus keeping transportation costs high and limiting the amount of saleable product shipped. Dewatering magnesium hydroxide slurries to a solids content of greater than about 60%, however, has proven impractical. Furthermore, the shelf life with respect to stability of the slurry still remains a problem.